/*
 * Copyright (c) 2007, 2015, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: SlotAllocator.java,v 1.2.4.1 2005/09/05 11:32:51 pvedula Exp $
 */

package com.sun.org.apache.xalan.internal.xsltc.compiler.util;

import com.sun.org.apache.bcel.internal.generic.LocalVariableGen;
import com.sun.org.apache.bcel.internal.generic.Type;

/**
 * @author Jacek Ambroziak
 */
final class SlotAllocator {

  private int _firstAvailableSlot;
  private int _size = 8;
  private int _free = 0;
  private int[] _slotsTaken = new int[_size];

  public void initialize(LocalVariableGen[] vars) {
    final int length = vars.length;
    int slot = 0, size, index;

    for (int i = 0; i < length; i++) {
      size = vars[i].getType().getSize();
      index = vars[i].getIndex();
      slot = Math.max(slot, index + size);
    }
    _firstAvailableSlot = slot;
  }

  public int allocateSlot(Type type) {
    final int size = type.getSize();
    final int limit = _free;
    int slot = _firstAvailableSlot, where = 0;

    if (_free + size > _size) {
      final int[] array = new int[_size *= 2];
      for (int j = 0; j < limit; j++) {
        array[j] = _slotsTaken[j];
      }
      _slotsTaken = array;
    }

    while (where < limit) {
      if (slot + size <= _slotsTaken[where]) {
        // insert
        for (int j = limit - 1; j >= where; j--) {
          _slotsTaken[j + size] = _slotsTaken[j];
        }
        break;
      } else {
        slot = _slotsTaken[where++] + 1;
      }
    }

    for (int j = 0; j < size; j++) {
      _slotsTaken[where + j] = slot + j;
    }

    _free += size;
    return slot;
  }

  public void releaseSlot(LocalVariableGen lvg) {
    final int size = lvg.getType().getSize();
    final int slot = lvg.getIndex();
    final int limit = _free;

    for (int i = 0; i < limit; i++) {
      if (_slotsTaken[i] == slot) {
        int j = i + size;
        while (j < limit) {
          _slotsTaken[i++] = _slotsTaken[j++];
        }
        _free -= size;
        return;
      }
    }
    String state = "Variable slot allocation error" +
        "(size=" + size + ", slot=" + slot + ", limit=" + limit + ")";
    ErrorMsg err = new ErrorMsg(ErrorMsg.INTERNAL_ERR, state);
    throw new Error(err.toString());
  }
}
